Recently, organic EL display devices have been put into practice. In mass-production of middle- or small-sized organic EL display devices performed today, an organic EL layer is formed mainly by use of vacuum vapor deposition. The organic EL layer includes, for example, a hole transfer layer, an electron transfer layer, and an organic light emitting layer located between the hole transfer layer and the electron transfer layer. The hole transfer layer may also act as the organic light emitting layer. Herein, a layer that includes at least an organic light emitting layer and an electron transfer layer and is formed of an organic material will be referred to as an “organic EL layer”.
An organic EL display device includes, in each of pixels, at least one organic EL light emitting element (Organic Light Emitting Diode (OLED)) and at least one TFT (Thin Film Transistor) controlling an electric current to be supplied to the corresponding OLED. Hereinafter, the organic EL display device will be referred to as an “OLED display device”. The OLED display device including a switching element such as a TFT or the like in each of the OLEDs as described above is referred to as an “active matrix OLED display device”. A substrate including the TFT and the OLED will be referred to as an “element substrate”. A driving circuit including the TFT is referred to as a “backplane circuit” (or simply as a “backplane”). The OLED is provided on the backplane.
In an organic EL display device capable of providing color display, one color display pixel includes, for example, an R pixel, a G pixel and a B pixel. The pixels of different colors included in the color display pixel may each be referred to as a “primary color pixel”. A pixel in this specification may be called as a “dot”, and a color display pixel in this specification may be called as a “pixel”. For example, “ppi” (pixel per inch) representing the resolution represents the number of “pixels” included in one inch.
In the case where one color display pixel includes three pixels of different colors, the three pixels of different colors may have different shapes or different sizes from each other. For example, a blue pixel having a low light emission efficiency may be large, whereas a green pixel having a high light emission efficiency may be small. Alternatively, one color display pixel may include one red pixel, one green pixel and two blue pixels. The pixels may be arrayed in a stripe form, a delta form or any of various known forms.
The organic EL layer is formed by vacuum vapor deposition by use of a deposition mask prepared for each of the colors. In addition to the organic EL layer, an electrode layer (e.g., cathode layer) on the organic EL layer may also be formed by use of a deposition mask by, for example, sputtering. The electrode layer (e.g., anode layer) below the organic EL layer may be formed by photolithography because the organic EL layer is not exposed to a developing solution.
Conventionally, a metal mask formed of a metal layer (metal plate) including a plurality of openings of a predetermined pattern is used as a deposition mask (e.g., Patent Document 1). In order to be more suitable to a higher-definition OLED display device, a deposition mask including a stack body in which a resin layer and a magnetic metal layer are stacked on each other has been proposed as a deposition mask allowing a more precise pattern than that of the metal mask to be formed therein (hereinafter, such a deposition mask including a stack body will be referred to as a “stack-type mask”) (e.g., Patent Documents 2 and 3).
In this specification, among members of a deposition mask, a member including openings (through-holes through which a substance used to form a film may pass) will be referred to as a “mask substrate”. In a metal mask, a metal layer (typically, a magnetic metal layer) is the mask substrate. In a stack-type mask, a stack body of the resin layer and the magnetic metal layer is the mask substrate. Among portions of a deposition mask, a portion that is to closely contact with an active region (also referred to as an “element formation region” or a “display region”) of the element substrate, which is an object on which a film is to be formed (for example, an element substrate on the stage where a backplane is formed), will be referred to as an “active region formation portion”.